Java学习的第三十七天

1.例3.1求一元二次方程的根

import java.util.Scanner;
public class cjava {
public static void main(String[]args) {
 float a,b,c,x1,x2;
 Scanner con=new Scanner(System.in);
 System.out.println("输入a,b,c的值:");
 a=con.nextInt();
 b=con.nextInt();
 c=con.nextInt();
 x1=(float)((-b+Math.sqrt(b*b-4*a*c))/(2*a));
 x2=(float)((-b-Math.sqrt(b*b-4*a*c))/(2*a));
 System.out.println("x1*"+x1);
 System.out.println("x2*"+x2);
}

3.2求三角形面积

package bgio;
import java.util.Scanner;
import java.lang.*;
public class cjava {
public static void main(String[]args) {
float a,b,c,x1,x2;
double s,area;
Scanner g=new Scanner(System.in);
System.out.println("输入a,b,c的值");
a=g.nextInt();
b=g.nextInt();
c=g.nextInt();
if(a+b>c&&b+c>a&&a+c>b) {
    s=(a+b+c)/2;
    area=Math.sqrt(s*(s-a)*(s-b)*(s-c));
    System.out.println("area="+area);
}
else
    System.out.println("it is not a trilateral!");
}
}

3.3判断字符大小写，大写转换为小写，小写不转换

package bgio;
import java.util.Scanner;
public class cjava {
public static void main(String[]args) {
char ch;
Scanner g=new Scanner(System.in);
System.out.println("请输入ch:");
String s;
s=g.next();
ch=s.charAt(0);
if(ch>='A'&&ch<='Z') {
    ch+=+32;
    System.out.println(ch);
}
else
    System.out.println(ch);
}
}

2.java.lang.*不明白

3.明天继续写例题